The functional architecture of endogenous and exogenous attention: a dynamic causal modeling study

Behavioral and electrophysiological studies have consistently supported a dissociation between endogenous (voluntary) and exogenous (involuntary) attention, whereas functional magnetic resonance imaging (fMRI) studies have generally found highly similar patterns of activity in the dorsal fronto-parietal network across these types of attention. The sluggish nature of the hemodynamic response, however, may obscure important timing differences across regions when fMRI is used. Indeed, single-unit recordings in macaque monkeys (Buschman & Miller 2007) suggested critical differences in the temporal order of frontal and parietal activities when comparing endogenous and exogenous attention. Here, we use dynamic causal modeling (DCM; Friston et al. 2003) in healthy human participants who performed visual attention tasks to investigate potential differences in directed connectivity across frontal-parietal regions between attention types. A priori regions of interest were centered on the bilateral frontal eye fields and intraparietal sulci. Bayesian comparison of competing model architectures for each condition revealed a consistent winning model, supporting a common underlying network. However, the modulatory effects of attention differed significantly across conditions. For example, leftward-oriented attention increased connectivity in the right hemisphere in both directions, though frontal-to-parietal connectivity increased significantly more during endogenous attention while the reverse was true for parietal-to-frontal connectivity. Interestingly, differences between conditions were only consistently observed in the hemisphere contralateral to the direction of orienting, suggesting that differences in effective connectivity between the two types of attention were driven largely by activity in the contralateral hemisphere.